In many articles of commerce, particularly consumer products, it is desirable to separate certain ingredients, yet have them disposed in a common container. Separation is particularly beneficial where one or more ingredients have negative interactions with each other. For example, in laundry detergents, enzymes are useful in removing stains but it is also best to separate them from other constituents, such as sources of alkalinity and surfactants, especially anionic surfactants like linear alkylbenzene sulfonates or alkyl sulfates. Bleaches, vitamins, perfumes, vegetable oils, plant extracts and ceramides are further examples of ingredients that sometimes need to be separated from the rest of the composition.
A known technique for separating ingredients in a common container includes encapsulation. Encapsulation technology is well known for different applications. Generally, encapsulation includes a medium that surrounds at least one component and thereby provides a barrier between the “encapsulated” component and other components. The barrier is typically temporary and is designed to break down and release the encapsulated material at a desired time, such as at a particular temperature, upon reaction or dissolution with chemicals, or due to mechanical stress. Methods of encapsulation include coacervation, liposome formation, granulation, coating, emulsification, atomization and spray-cooling.
WO 92/20771 discloses particles having a substantially anhydrous core comprising a matrix polymer containing active ingredient, a layer of hydrophobic oil around the core and a shell of polymer around the oil layer. The process for making the particles includes the steps of dispersion in oil of particles of a matrix polymer containing active ingredient, dispersing this dispersion into the aqueous solution and causing a solid polymer shell to form around the droplets of the matrix particles.
Norbury et al. (U.S. Pat. Nos. 4,976,961 and 5,013,473) disclose the addition of a polymer (which may be a polystyrene-polybutadiene-polystyrene block copolymer, e.g. Kraton® 1107) or a wax to an oil phase to increase the viscosity of the oil. The oil-polymer phase forms a core of the Norbury capsule; shell material is formed from another polymer.
Falholt et al. (U.S. Pat. No. 4,906,396, UK 2 186 884, and EP 0 273 775) disclose a protective enzyme system, wherein enzymes are dispersed in a hydrophobic material which is an organopolysiloxane oil or a high molecular weight hydrocarbon including a solid or waxy material. Especially preferred are said to be hydrophobic liquids which had been stabilized by suspending therein hydrophobic solid particles such as hydrophobic silica.
Mitchnick et al. (U.S. Pat. No. 5,733,531) disclose a cosmetic sun-blocking composition containing particles which include a matrix and a UV-attenuating compound incorporated into the matrix. A preferred encapsulating matrix comprises wax. Certain polymeric materials may also be employed.
Ratuiste et al. (U.S. Pat. No. 5,589,370) discloses a process for encapsulation of sensitive materials, the capsule containing an oil dispersion holding an active and an outer polymer shell surrounding the oil dispersion. Tsaur et al. (U.S. Pat. Nos. 5,441,660 and 5,434,069) also disclose a capsule containing an oil dispersion containing an active and the polymer shell surrounding the dispersion. Another patent by Tsaur et al. (U.S. Pat. No. 5,498,378) discloses wax capsules containing a structuring agent which may be a hydrophobic silica, a hydrocarbon material and organophilic clay. An example of a high molecular weight hydrocarbon is given as a hydrocarbon rubber or elastomers.
Morrison et al. (U.S. Pat. No. 5,879,694) discloses transparent stiff gel candles comprising a hydrocarbon oil and a block co-polymer of a thermoplastic rubber (e.g., Kraton® series of polymers).
Despite numerous capsules in the prior art, a problem remains to produce a commercially attractive capsule which is stable—the encapsulated ingredient should not leach out of the capsule upon storage (especially important is the stability of capsules in liquid compositions)—but should release the protected ingredient with ease during normal use. An additional challenge is that the capsules need to be manufactured with relative ease. For instance, in some prior art capsules the melt temperature of the encapsulating material may damage the encapsulated material during the encapsulation process.
An additional, more specific, problem with capsules for consumer products is the manufacture of either transparent or colored capsules. The encapsulating material, e.g. wax, is typically opaque. In such capsules, when the encapsulated ingredient is a colorant, the opaque shell obscures the colored core. Yet, it is frequently desirable to produce a colored capsule to increase the appeal of the consumer product. Including the colorant into the shell material, however, reduces the choice of colorants to oil-soluble colorants (since most encapsulating materials are hydrophobic). Thus, in order to produce colored capsules, it is desirable to encapsulate a water-soluble dye in the transparent shell.